It is common practice to electrochemically etch aluminum foil to increase the surface area thereof for capacitor electrodes. In the United States and Europe this is usually done with direct current while in Japan it is commonly done with alternating current. A modified type of direct current called pulsating or ripple direct current has also been used. With this type of current a particular wave shape is superimposed on a steady direct current.
Most of the prior art patents on alternating current electrochemical etching of aluminum do not specify wave shape or frequency of the current, giving rise to the implication that the use of ordinary line current at 50 or 60 hz is suitable, although recently a Japanese process has been reported with low frequency alternating current of 3 to 30 hz.